1. Field of the Invention
This invention relates to wide bandgap materials and more particularly an article comprising a high crystalline quality layer formed in a wide bandgap material and the method of forming a high crystalline quality layer. The invention relates further to an improved component such as wide bandgap semiconductor device formed within the high crystalline quality layer.
2. Background of the Invention
Presently, silicon and gallium arsenide are the dominant conventional semiconductor materials used in the manufacture of semiconductor devices. Silicon and gallium arsenide are considered non-wide bandgap semiconductors. In contrast, wide bandgap semiconductors have superior properties including breakdown field, dielectric constant, thermal conductivity and saturated electron drift velocity. Unfortunately, wide bandgap semiconductors are expensive due to high processing costs and poor yields emanating from wafer growth through device packaging.
Ceramic substrates having wide bandgap semiconductor compositions, such as silicon carbide (SiC) and aluminum nitride (AlN), are known to exhibit electrical properties ranging from insulating electrical properties, semiconducting electrical properties and conducting electrical properties.
The wide-bandgap semiconductor phases of ceramics and other wide-bandgap semiconductors including diamond are used to create devices such as conductive tabs, interconnects, vias, wiring patterns, resistors, capacitors, semiconductor devices and the like electronic components by laser synthesis on the surfaces and within the body of such wide-bandgap semiconductors to thereby eliminate photolithography processes which require numerous steps and generate undesirable chemical pollutants when processing such traditional electronic devices, components and circuitry.
It is well known that alumina (Al2O3) dominates the dielectric market as an integrating substrate or device carrier in electronics packaging. Boron nitride (BN), aluminum nitride (AlN), silicon carbide (SiC) and diamond are also of interest due to the thermal coefficient of expansion (TCE) and for the dielectric constant and higher thermal conductivity than that of aluminum oxide (Al2O3). Silicon carbide (SiC), aluminum nitride (AlN), boron nitride (BN), gallium nitride (GaN) and diamond also exhibit a wide-band gap and chemical resistance as well as exhibiting properties from a semiconductor to an insulator. These properties are of substantial interest for high temperature applications approaching 1000° C. and for aggressive environment applications. In addition, these properties are desirable for high density integrated circuit packing.
In the prior art, metallization methods, including dry-film imaging and screen printing have been used for the production of conductive patterns on alumina. However, metal compatibility difficulties with high thermal conductivity ceramic materials such as aluminum nitride (AlN) and silicon carbide (SiC), have not been completely solved. Copper and silver paste exhibits a thermal coefficient of expansion (TCE) mismatch aggravated by high temperatures as well as being subject to oxidation that increases the resistivity. In particular, bonding of copper to aluminum nitride (AlN) has proved to be nontrivial. Alumina or stoichiometric aluminum oxynitride (AlON) coatings must be developed on the aluminum nitride (AlN) surface through passivation processes. These passivation processes have poor reproducibility. Thus, the direct laser synthesis of conductors in aluminum nitride (AlN), silicon carbide (SiC) and diamond substrates appears to provide solutions to this long standing prior art problem with regard to metallization and for more simple processing techniques for creating devices and circuitry that are compatible with selected ceramic substrates, while satisfying the need for higher temperature, aggressive environment, and higher density integrated circuit packaging applications.
Many commerically available wafers of wide band gap material contain impurities such as substitutional atoms, and numerous lattice defects including lattice vacancies, dislocations and micropipes. These impurities and lattice defects result in a low resistivity for the wide bandgap material. The low resistivity makes the wide bandgap material unsuitable as a defect free intrinsic semiconductor for fabricating defect free devices and isolating devices.
One example of a commercially available wide band gap material is silicon carbide wafer SiC. A conventionally processed silicon carbide SiC wafer contains processed induced defects including 1) carbon vacancies created by the displacement of carbon atoms from lattice to interstitial sites, 2) substitutional nitrogen atoms located in the carbon vacancies, 3) dislocations, 4) stacking faults and 5) micropipes. The above defects render the silicon carbide wafer SiC unsuitable for use as a defect free intrinsic semiconductor for fabricating defect free devices and isolating devices.
One conventional approach is to create a high quality layer or thin film on the wide bandgap material. An external layer (epitaxy layer) is deposited upon an external surface of the commercially available wafers of the wide bandgap material. Typically, the external layer (epitaxy layer) is applied to the external surface of the commercially available wafers by chemical vapor deposition (CVD), molecular beam epitaxy (MBE) or liquid phase epitaxy techniques. The wafers of wide bandgap material serve as a seed substrate and the external layer (epitaxy layer) is grown on top of the seed substrate. Unfortunately, defects and/or impurities in the underlying wide bandgap material can migrate or travel into the external layer (epitaxy layer).
Completely different methods of processing material such as wide bandgap materials are discussed in U.S. Pat. No. 5,145,741; U.S. Pat. No. 5,391,841; U.S. Pat. No. 5,793,042; U.S. Pat. No. 5,837,607; U.S. Pat. No. 6,025,609; U.S. Pat. No. 6,054,375; U.S. Pat. No. 6,271,576, U.S. Pat. No. 6,670,693, U.S. Pat. No. 6,930,009 and U.S. Pat. No. 6,939,748 are hereby incorporated by reference into the present application.
The prior invention disclosed in U.S. patent application Ser. No. 11/062,011 filed Feb. 18, 2005 and U.S. Provisional application Ser. No. 60/546,564 filed Feb. 19, 2004 disclosed an apparatus and a process for forming a layer of a wide bandgap material in a non-wide bandgap material. The present invention seeks to improve upon the prior invention disclosed in U.S. patent application Ser. No. 11/062,011 and U.S. Provisional application Ser. No. 60/546,564.
Therefore, it is an object of the present invention to provide an apparatus and method for forming a high crystalline quality layer (endolayer) within a wide bandgap substrate.
Another object of this invention is to provide an apparatus and method for forming a high crystalline quality layer (endolayer) integral within the wide bandgap substrate.
Another object of this invention is to provide an apparatus and method for forming a high crystalline quality layer (endolayer) within a wide bandgap substrate suitable for use as a defect free intrinsic semiconductor material.
Another object of this invention is to provide an apparatus and method for forming a high crystalline quality layer (endolayer) within a wide bandgap substrate and for subsequently forming a component within the high crystalline quality layer (endolayer).
Another object of this invention is to provide an apparatus and method for forming a high crystalline quality layer (endolayer) within a wide bandgap substrate that forms a continuous or diffuse boundary as opposed to a discrete boundary and matches the thermal coefficient of thermal expansion of the parent substrate that prevents introduction of mobile defects into the endolayer.
Another objective of this invention is to provide a defect free intrinsic wide bandgap semiconductor material for defect free devices and device isolation.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed as being merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by modifying the invention within the scope of the invention. Accordingly other objects in a full understanding of the invention may be had by referring to the summary of the invention, the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.